I have a Lenovo X60t Tablet PC running Ubuntu Linux. I usually print my character to PDF (I have my own way of doing it, but somehow getting two pages per sheet is ideal) from the character builder (running in a virtual machine), then open it up with Xournal (not sure what the equivalent is for XP, but I'm sure there is something). You can then draw on it like a normal character sheet. So far, this seems to be the best way for me to play 4e D&D.
Edit: Oops didn't see this was for 3.x.. Probably doesn't apply. My bad!